Recently, considerable attention has been given to the observed increase in skin cancer attributed in part to people's lifestyles and leisure activities that result in excessive and prolonged exposure to harmful ultraviolet (UV) light rays present in solar radiation. The UV rays have been divided into three regions: UV-A Region (320-400 nm), UV-B Region (290-320 nm) and UV-C Region (200-290 nm). The UV-C Region has the highest energy and most damaging radiation, but is largely absorbed by the ozone layer. UV light in the UV-B Region, also called the Erythemal or Burning Region, causes sunburn and is responsible for most of the immediate damage to the human body, i.e., skin and hair. UV-A Radiation, also called the Tanning Region, causes tanning but also may cause many other harmful biological effects, such as DNA damage and the formation of dermal cysts (Cosmetics and Toiletries, Vol 115, No 6, p 37-45 (2002), and references therein).
Many Personal Care products contain materials that absorb the harmful ultraviolet light to protect the skin from damage. Early formulations of these contained UV light-absorbing chemicals capable of absorbing most of the UV-B light, but little of the UV-A light. Because of the harmful effects of UV-A radiation most formulations now include a combination of UV-A and UV-B light absorbing compounds. Because some of the active ultraviolet light absorbers are destroyed by ultraviolet radiation, many formulations contain stabilizers that also absorb ultraviolet radiation. See, for example, N. A. Shaath, Cosmetics and Toiletries, 101, March 1986, pp 55-70; Consumer Reports, June 1988, pp 370-374, and Chemical and Engineering News, Apr. 11, 2005, pp 18-22. These modern formulations have been designed to absorb most of the UV light in the range of 280 to 400 nm, particularly in the 280 to 360 nm range which contains the most damaging UV light. Modem formulations are also designed to remain stable to ultraviolet light for several hours after their application to the skin.
Many ultraviolet light absorbers for personal care are small organic molecules with molecular weights below 600 amu's. A significant body of evidence shows that many of these molecules can penetrate the skin, and recent work indicates that once this occurs—absent a reapplication of the sunscreen—their presence in the skin may cause more free-radical induced damage than that observed in untreated skin. See Hanson et al, Free Radical Biology and Medicine, Volume 41, Issue 8, 2006, pp 1205-1212.
Large molecules, on the other hand, are known not to easily penetrate the skin (Experimental Dermatology, 2000, Vol 9, pp 165-169) so polymeric ultraviolet absorbers cannot cause the cellular damage possible for ultraviolet light absorbers which are small molecules.
The objective of this invention is to provide polymeric UV absorbing materials that can absorb either UV-A radiation or a combination of UV-A and UV-B radiation, that contain a high concentration of the UV-absorbing moieties, and that do not penetrate the skin.
Polymeric ultraviolet light absorbers are known. UV-absorbing chromophores have been incorporated into polyesters (U.S. Pat. Nos. 5,243,021, 5,374,419), polyamides (U.S. Pat. No. 3,864,473), polyester-polyamide copolymers (U.S. Pat. No. 5,698,183), silicone-containing polymers (U.S. Pat. Nos. 5,495,039, 6,068,929, 6,114,559, 6,193,959), and polyaminoamides (U.S. Pat. No. 6,887,400). Polyanhydride resins have also been reacted with UV absorbers capable of reacting with anhydride moieties (US published application 20050191249 A1).
UV absorbers have also been functionalized with groups capable of undergoing a vinyl polymerization. Homopolymers (U.S. Pat. Nos. 3,313,866, 5,099,027 5,843,410) and various copolymers with maleic anhydride (U.S. Pat. No. 5,869,099), acrylic acid or its derivatives (U.S. Pat. Nos. 3,529,055, 4,233,430, 4,524,061, 4,839,160, 4,528,311, 5,063,048, 6,123,938, 7,008,618), substituted styrenes (U.S. Pat. Nos. 5,843,410, 7,087,692), vinyl esters of carboxylic acids (U.S. Pat. No. 6,143,850), and vinyl thioacetate (U.S. Pat. No. 4,004,074) have been disclosed.
All of the above polymeric ultraviolet light absorbers suffer either due to low concentration of the UV absorbing moiety in the polymer or due to the absorption of light in only a narrow portion of the UV region.